Konstantinos Pachnis wrote:
I'm curious if RAID 1 (mirroring) really helps to protect data loss.
Of course if a whole disk "dies", RAID 1 has the advantage that
I have an identical copy. But what happens if only a sector of one disk
contains bad data. How can the RAID controller decide which is the
correct sector? Or would the disk detect such a case and return an
error?
When the controller will try to perform an I/O operation it will fail on
the faulty disk (the disk with the bad sector). As a result the
controller will be able to decide which is the correct sector.
You're assuming fail-stop errors. If it is a sneaking bit error or
something else, it won't notice.
cheers
simon
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